GROUND COVER
PRECISION AGRICULTURE
19
contains three obvious zones. These have no
relation to the management zones defined on
the basis of soil properties except that one of
them coincides with the area that was cleared
after 2001. In the eastern part of the paddock,
the northern section is obviously different to
the southern section in a way that can't be
explained from the soil parameters.
Two things are clear. The first is that,
on the Red-Blue index map, more of the
northern section shows less intense flower-
ing, mapped as red-orange, and the headland
area around the southern area seems similar
to this.
The second is that the boundary between
the northern and southern areas is a straight
line parallel to the direction of sowing,
which suggests the difference is man-made.
This difference is actually due to a three-day
interruption to sowing because of rain. The
small, separate block at the northern end
of the paddock and the southern end of the
main block were sown first and before it
rained. The northern part of the main block
and the headland around the southern part
were sown a few days later when the soil
had dried enough after the rain.
The only "natural" variation appearing in
the map of Red-Blue index is due to the lens
of red soil in the north-east of the paddock.
Here the value of the index shows mid-range
flowering and is visible as a green area dis-
tinctly different to the rest of the later sown
section.
The bulk of the variation in the "flower-
ing" image can thus be explained by events
within the current season or in previous
seasons. In this case, the difference in time of
clearing of the northern section explains the
variation in the early sown part of the pad-
dock and sowing time explains most of the
remaining variation.
Paddock history can be an important fac-
tor in explaining variation observed in crop
imagery and may even outweigh natural fac-
tors such as major soil variations. This must
be kept in mind when maps of yield variation
are being analysed to identify the underlying
causes, and emphasises the value of using
several years of biomass and/or yield data,
over different crops and seasons, when assess-
ing the value of using paddock management
zones.
GRDC Precision Agriculture Initiative (SIP09)
GRDC Research Code DAN00054
For more information: Alan Palmer,
08 6880 8058, alan.palmer@dpi.nsw.gov.au
Figure 2:
Map of the
draught of
a seeder
point at the
Trangie-
Tottenham
site, May
2004.
Figure 1
(top and
middle):
enhanced
aerial
images of
the site in
the Trangie-
Tottenham
area.
2001: five-colour classification of aerial photograph of bare-soil.
2004: Red-Blue Index of flowering canola from multi-spectral image.
No data
1 -- Lowest
2
3
4
5
6
7
8 -- Highest
> 1.36kN
1.26 -- 1.36kN
1.17 -- 1.26kN
1.08 -- 1.17kN
< 1.08kN
Draught of superseeder-point
75 mm deep
150 300 450 600
metres